Honing machine with stroke length control



Feb. 20, 1968 M. R. ESTA-BROOK 3,369,327

HONING MACHINE WITH STROKE LENGTH CONTROL Filed Sept. 17,1965

2 Sheets-Shem l Illilrll 5 M. R. ESTABROOK HONING MACHINE WITH STROKE LENGTH CONTROL Filed Sept. 17, 1965 P Sheets-Sheet 13 wwomsybf United States Patent 3,369,327 HONING MACHINE WITH STROKE LENGTH CONTROL Mark R. Estabrook, Rockford, Ill., assignor to Barnes Drill C0., Rockford, 111., a corporation of Illinois Filed Sept. 17, 1965, Ser. No. 488,008 12 Claims. ('Cl. 51-34) This invention relates to an automatic machine for honing the wall of a bore by reciprocating and simultaneously expanding an abrading tool therein, and relates more particularly to the control of the reciprocation of the tool within the bore.

In such machines, it is customary to operate the reciprocating actuator in response to reversal signals produced as the tool is approaching, and is a predetermined distance from, the end of each stroke. The reversing control operates the actuator in time to overcome the momentum of the tool head in one direction and stop the head when the tool reaches the desired reversal point. In practice, however, it has been found that the length of the stroke becomes progressively shorter as the cycle progresses, apparently as a result of the increasing drag produced by the increasing force exerted by the tool on the bore wall and the effect of this greater drag in overcoming the momentum of the head prematurely. While the actual amount by which the stroke is shortened is small, the effect on the ability to hone to within close tolerances throughout the length of the bore can be significant.

Accordingly, the general object of the present invention is to maintain the length of stroke constant throughout the honing cycle despite the increasing drag on the tool and thereby improve the capability of the machine to hone within close tolerances.

A more detailed object is to sense the increasing honing force throughout the cycle and automatically increase the delay in reversal of the reciprocating actuator progressively and in direct relation to the increasing force thereby to counteract variations in the drag effect of the honing force.

Another object is to accomplish the foregoing in a relatively simple manner.

Still another object is to utilize a conventional reciprocation control and operate the same in a novel manner in response to the sensed increase in honing force to avoid shortening of the stroke.

Other objects and advantages of the invention will become apparent from. the following detailed description taken in connection with the accompanying drawings, in which FIGURE 1 is a schematic view showing the primary components of a honing machine together with a fragmentary schematic diagram of a control embodying the novel features of the present invention.

FIG. 2 is an enlarged fragmentary cross-sectional view taken substantially along the line 2-2 of FIG. 1.

FIG. 3 is an enlarged fragmentary view of part of the control, the valves of the control being shown mostly in section for clarity of illustration.

FIG. 4 is a fragmentary view of a portion of FIG. 3 in a moved position.

As shown in the drawings for purposes of illustration, the invention is embodied in an automatic honing machine for removing surface roughness from the wall (FIGS. 1 and 2) of a bore in a workpiece 11 while enlarging the bore to a preselected size by reciprocating an abrading tool 12 back and forth through the bore and simultaneously rotating the tool with the abrasive surfaces 13 thereof pressed against the wall. As the wall is worn away and the bore is enlarged, the tool is expanded to maintain working pressure until the bore attains the desired size.

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In this instance, the machine is of the vertical type in which the tool 12 is carried on the lower end of an elongated hollow spindle 14 journaled at its upper end on a head 15 slidable up and down along vertical guides (not shown) and rotated relative to the head by an electric motor 17 connected by gearing 18 to a drive shaft 19 geared at 20 to the upper end of the spindle. Reciprocation of the head through forward and return strokes is produced by a reciprocating hydraulic actuator 21 herein comprising a stationarily mounted cylinder 22 with a piston 23 guided therein for up and down movement and connected to the head by a rod 24 projecting through the upper end wall of the cylinder. Lines 25 and 27 communicate respectively with the head end 28 and the rod end 29 of the cylinder to deliver pressure fluid from a suitable source to the cylinder through a reciprocation control indicated generally at 30 and herein including a valve 31 which alternates the flow of pressure fluid to the cylinder and thus controls the reciprocation of the head and the tool.

The tool 12 is of a conventional type comprising a hollow, generally cylindrical body having a coaxial shank 3-2 at one end fastened to the lower end of the spindle '14, the body being formed with a plurality of angularly spaced longitudinal slots in which honing elements 33 (FIG. 2) are carried. Each honing element includes a stick or stone 34 of bonded abrasive material disposed with a snug fit in one of the slots with the outer face of the stone forming an abrasive surface 13 engageable with the bore wall 10. Expansion of the tool during honing is produced by an expander disposed within the hollow tool body and formed with two conical earns 35 engaging followers 37 projecting inwardly from backing bars 38 carrying the honing stones, the followers being held against the cams by garter springs 39 in notches 40' at the ends of the backing bars. With this conventional arrangement, downward movement of the expander feeds the honing elements outwardly to expand the tool, and upward movement of the expander permits contraction of the tool.

Controlled expansion of the tool 12 during the honing cycle is produced by a drive mechanism 41 on the head 15 connected to the expander cams 35 by a so-called push rod 42 connected at its lower end to the expander and extending upwardly through the hollow spindle 14 into the head. While the drive mechanism may take different well-known forms, herein it comprises an electric motor 43 (FIG. 1) driving a worm 44 meshing with a worm wheel 45 on a shaft 47 perpendicular to the motor shaft and carrying a second worm 48 meshing with a worm Wheel 49 on a shaft 50 coupled by a selectively engageable clutch 51 to an output shaft 52. The latter drives a worm 53 meshing with a worm wheel 54 formed on a sleeve 55 internally threaded onto a screw 57 on the upper end of the push rod thereby forming a screw device for converting the rotary motion of the feed motor and its reduction gearing into relatively slow endwise motion of the push rod and slow outward feeding of the stones 34.

In the illustrative machine, the feed motor 43 is a DC. motor with its armature 58 receiving DC. current from a rectifier 59 connected across two A.C. power lines 60* and 6 1. One terminal of the motor armature is connected to the positive output side of the rectifier by a line 62 and the other armature terminal is connected through a line 63 to a line 64 connected to the negative side of the rectifier. The motor field winding 65 is supplied with DC. current by a second rectifier 67 connected across the A.C. power lines. A variable transformer 68 selectively adjusts the field strength and thus the torque capacity of the motor which may be of any desired size, for example, HP. The D.C. input voltage preferably is on the order of volts.

A second motor 69 is geared at 7t} directly to the output shaft 52 to shift the honing elements 33 at rapid traverse rates toward and away from the bore. wall 10. The clutch 51 is engaged during operation of the feed motor 4 3 and disengaged during operation of the traverse motor 69 which simply turns idly during slow feeding of the honing elements. This arrangement and the automatic controls for its operation are well known to those skilled in the art.

The control valve 31 is a standard four-way valve having an inlet port 71 intermediate its ends, spaced outlet ports 72 and 73 adjacent its opposite ends communicating respectively with the lines and 27, and a spool slidably guided for back and forth movement between a forward or down position shifted to the right, and a reverse or up position (FIGS. 1 and 3) shifted to the left. Thus the spool moves through an intermediate reversing position. In the down position, the spool establishes communication between the inlet port and the outlet port 73 to deliver pressure fluid from a supply line 74 through the line 27 to the rod end 29 of the cylinder 22, and in the up position, the inlet port communicates with the other outlet port 72 to deliver pressure fluid to the line 25 and the head end 28 of the cylinder. Exhaust flow from the cylinder returns through the idle line and the control valve to an exhaust line 75 communicating with both exhaust ports 77 of the valve.

The control 30 operates the control valve 31 in response to reversal signals produced in a Well-known manner by a control disk '79 (FIG. 1) fast on a shaft 80 geared at 81 to a second shaft 82 carrying a sprocket 83 around which a flexible chain 84 is trained, the chain being fastened at both ends to the head 15 and also trained around a second sprocket (not shown) above the head. Accordingly, the disk oscillates about the axis of its shaft in unison with the up and down motion of the head. Pivoted on the shaft alongside the disk is an arm 85 which is disposed between two lugs 87 and 88 on the periphery of the disk and is rocked back and forth about the shaft axis by the lugs. As the disk turns clockwise during the down stroke of the head, the lug 87 picks up the arm 85 and carries it clockwise with the disk until the free end of the arm engages the operator 89 of a pair of companion switches 90 and 90 closing the switch 90 and opening the other. As the disk turns counterclockwise during the up stroke, the lug 88 picks up the arm, rocking it counterclockwise and away from the switch operator to permit the switch 90 to open while the switch 90 closes. The two lugs are positioned to close the switch 90 each time the head 15 approaches the end of its down stroke and close the switch 90 as the head approaches the end of the up stroke thereby signaling the need for reversal of the direction of movement of the tool 12.

Although the reversal signals are produced simultaneously with the closure of the switches 90, 90, actual reversal of the head 15 necessarily is delayed due to the time required to shift the control valve spool from one position to the other, and also due to the necessity of overcoming the momentum of the head in one direction and bringing it to a stop before it can be reversed. For these reasons, the signal switches are operated before the tool 12 reaches the end of each stroke, and when the tool is a preselected distance from the end, so that the tool motion actually reverses at a desired point beyond the signal point. In other words, there is a calculated overshoot beyond the points where the signal switches are operated.

In practice, it has been found that the amount of over shoot varies with the magnitude of the honing force being exerted on the stones 34 through the push rod 42 and thus by the stones on the bore wall 10. As the force builds up, the stroke tends to become progressively shorter, apparently as a result of the increase in the frictional drag exerted by the bore wall on the tool. This drag is a material factor with respect to the time acquired to overcome the momentum of the head after the reversal signal is produced and the control valve is reversed. While the actual amount of shortening of the stroke in a honing cycle may be only a small fraction of an inch, the effect of this shortening on the bore size can be significant when the bore is to be honed within very close tolerances. Although the tool usually extends through and beyond the end of the bore at the end of both the forward and return strokes, shortening of the strokes results in less honing of the portion of the wall adjacent the ends and, consequently, removal of slightly less material from these areas. As a result, the intermediate portion becomes slightly larger in diameter than the end portions where the diameter usually is measured during honing, and thus will be slightly oversize when the end portions attain the desired size.

In accordance with the present invention, the stroke length is maintained constant throughout the honing cycle and despite the increasing frictional drag on the tool 12 by varying the delay in the operation of the control valve 31 automatically, relatively simply, and in direct relation to the magnitude of the prevailing honing force thereby compensating for the varying effect of the honing force in overcoming the momentum of the head 15 and bringing the latter to a stop. To this end, a signal device 91 senses and indicates the magnitude of the progressively increasing honing force exerted on the stones 34, and the signal produced by this device is used to vary the delay in operation of the reversing control in accordance with the magnitude of the force. As the force and the resulting drag become greater, the delay is correspondingly increased. This has the effect of permitting the head to move closer to each reversal point before the control attempts to reverse the direction of motion, thereby compensating for the progressively shortening distance necessary to accomplish the reversal.

In this instance, the force sensing and signaling device 91 is a tungsten-filament incandescent lamp connected in series with the armature 58 of the feed motor 43 so that the current drawn by the armature throughout the honing cycle flows through the lamp filament. Such filaments are non-linear resistors having positive temperature coeflicients of resistance. This means that the resistance of the filament increases with the filament temperature which, in turn, varies over a wide range with the current flow through the filament. Thus, variations in the voltage drop across the filament produced by the prevailing resistance level reflect variations in the rate of current flow through the filament and the armature. This rate, of course, is proportional to thetorque exerted by the motor and the resulting honing force. The use of two lamps in series will reduce the voltage across each lamp for increased life in service use. In the illustrative control, for example, the use of two bulbs rated at 150 watts, volts, is preferred.

In the typical honing cycle, the stones 34 first wear away the ridges and high spots on the 'bore wall 10 and encounter progressively increasing resistance to expansion, apparently as a result of the increasing area of engagement between the wall and the stones as the latter approach and begin working on base metal, the surface of a substantially smooth and cylindrical wall. Thus, the armature speed begins to drop and produces a corresponding increase in armature current and motor torque due to the progressively reduced back voltage generated by the armature. With the lamp 91 in series with the armature 58, this progressive current increase raises the resistance of the lamp filament, increases the voltage drop across the lamp in relation to the current increase, and thereby reduces the terminal voltage of the armature. Accordingly, the lamp is a force-responsive modulator for controlling the torque exerted by the feed motor automatically in response to the rate of increase in the resistance to expansion of the tool 12, as well as a device indicating the prevailing magnitude of the motor torque .5 and the resulting honing force exerted on the bore wall by the stones.

This varying signal is used to operate the reciprocation control 30 and obtain reversal of the head 15 at the same point at the end of each stroke. For this purpose, the control valve 31 is operated by a reversing valve 92 for delivering pilot-pressure fluid to the control valve to shift the spool therein, back and forth and the reversing valve is operated by an actuator 93 which varies the rate of flow of such pilot fluid in accordance with the magnitude of the prevailing force-level signal, reducing the rate progressively as the force level increases in order to re duce the rate of spool shift and thereby increase the delay in the reversal of the flow through the hydraulic actuator 21.

In this instance, the reversing valve 92 is formed with an inlet port 94 (FIGS. 3 and 4) communicating with the supply line 74 between the two heads 95 and 97 of the valve spool, and two outlet ports 98 and 99 adjacent the ends of the valve opening into pilot lines 100 and 101 leading to the control valve. The spool is guided in the valve for back and forth movement through a neutral centered position (FIG. 1) in which the inlet port is closed, and moves in both directions from this position to open one of two feed orifices 102, 103 communicating between the inlet 94 and one or the other of the outlets and the associated pilot lines. When the spool is displaced to the left (FIG. 4) from the centered position, pilot fluid flows through the orifice 1112 around the head 95 to the outlet 98 and the pilot line 100. In the opposite direction of displacement, fluid from the inlet flows through the orifice 103 around the head 97 to the outlet 99 and the line 101.

The pilot lines open into two pressure chambers 104 and 105 formed in the ends of the control valve body at the opposite ends of the control valve spool. Flow through the line 100 shifts the spool to the right from the position shown in FIG. 3, fluid being exhausted through the line 101, the reversing valve 92, and an exhaust port 107 therein. Flow through the line 101 to the chamber 105 shifts the spool to the left while fluid is exhausted from the chamber 104 through the other line and the exhaust port. The exhaust port communicates with the exhaust line 75. A valve 108 maintains high pilot pressure above the control valve.

As shown schematically in FIGS. 1 and 3, the actuator 93 or the reversing valve 92 is a torque motor having an armature 109 pivofally supported intermediate its ends on a shaft 110 with the opposite ends of the armature disposed between sets of opposed poles on two mag netic pole pieces 111 and 112 (FIG. 3). When the motor is deenergized, the armature is mechanically centered between the pole pieces, for example, by using a torsionally flexible shaft 110 which urges the armature to the position shown in FIG. 1 but is capable of twisting to permit rotation of the armature in response to the force applied when either of the armature coils 113, 114 is energized. These coils are connected in parallel across the two DC. power lines 62 and 6 -1 of the control circuit (FIG. 1) and are alternately energized through the switches 90 and 90 near the ends of the strokes of the head 15. The reversing control illustrated herein is a conventional unit sold by Minneapolis Honeywell as Part No. V7038Al051.

One end of the torque motor armature 109 is connected by a rod 115 to the spool of the reversing valve 92 as shown in FIG. 3 so that the rocking motion of the armature is transmitted to the spool as linear movement thereof. When the switch 90 closes to energize the coil 114, the armature turns clockwise to shift the spool to the left to the position in FIG. 4. Closure of the switch 90 energizes the coil 113 to rock the armature counterclockwise (see FIG. 3) and shift the spool to the right. Since the torque motor works against the biasing force exerted the shaft 110 in each direction, the amount of displace ment of the reversing valve spool from the centered/ 6 closed position (and, therefore, the degree of opening of the feed orifices 102, 103 around the heads 95, 97) depends upon the degree of energization of the motor 93 and the resulting control torque exerted. by the motor against the biasing force. By varying the control torque within a range correlated with the biasing force, the amount of spool displacement, the degree of opening of the feed orifices, the rate of flow to the pressure chambers 104- and 105, and, consequently, the rate of shift of the spool of the control valve 31 may be selectively controlled.

To energize the torque motor 93 in accordance with the prevailing force-level signal, the rate of current flow through the coils 113, 114 is progressively reduced as the voltage drop across the lamp 91 increases thereby reducing the control torque in direct relation to increases in the prevailing feed motor torque and honing force level. Herein, this progressive reduction in energizing current is obtained by applying a selected portion of the lamp voltage as an input voltage to the base of a transistor 116 (FIG. 1) in series with the torque motor coils. With this arrangement, the input voltage opposes the forward bias of the base-emitter junction so that increases in the lamp voltage reduce the controlled emitter-collector current, that is, the current that flows from a positive input line 117 through the closed switch 90 or 90 the active torque motor coil, and the transistor to line 64.

As shown in FIG. 1, the transistor 116 is of the PNP type with its collector connected to the .negative power line 64, its emitter connected between the coils 113 and 114, and its base connected to an input line 118 connected to the wiper of a potentiometer 119 in series with a voltage-dropping resistor 120 in a line 121 from the positive side of the lamp 91, between the latter and the armature 58, to the negative line 64. The resistor reduces the input voltage level at the potentiometer to within the range desired at the transistor for production of torque motor energizing voltages correlated with the biasing force of the shaft. A second resistor 122 connected in parallel with the transistor in effect limits the maximum voltage drop across the latter and preferably has the same resistance as the respective coils of the torque motor. For example, both may have resistances of 5000 ohms. Representative values for the voltage-dropping resistor 120 and the potentiometer 119 are 100,000 ohms and 50,000 ohms respectively.

At the beginning of the honing cycle, the tool 12 is collapsed and in the position shown in FIG. 1 above the workpiece 11 to be honed, the hydraulic pump (not shown) is running to make pressure fluid available in the supply line 74, and the control circuits are in the deenergized condition shown in FIG. 1, the switch being closed to prepare a circuit through the down coil 114 and the transistor 116 to energize the coil as soon as start switches 123 are closed. When these switches are closed and the down coil is energized, the armature 109 turns clockwise to shift the reversing valve spool to the left as shown in FIG. 4, opening the orifice 102 around the spool head to admit fluid from the supply line through the pilot line to the chamber 104 and thereby shifting the control valve spool to the right from the position shown in FIG. 1.

In this condition, fluid from the supply line 74 flows through the control valve 31 to the line 27 leading to the rod end 29 of the cylinder 22 to start the head 15 down. When the tool 12 is inside the bore 10, it is ex panded rapidly by the motor 69 to bring the stones 34 close to or against the bore wall, and the feed motor 43 is started in the usual manner to begin slow feeding of the stones. As the tool approaches the lower end of its stroke, the arm 85 engages the operator 89 and closes the switch 90 while opening the associated switch 9%.

shift the reversing valve spool to the right (FIG. 3). Thus, pilot fluid flows through the line 161 to the chamber 105 to shift the control valve spool to the left, thereby reversing the flow to the cylinder 22 and starting the piston 23, the head 1d and the tool 12 back up relative to the workpiece 11.

Initially, the resistance to expansion of the tool 12 is slight and the feed motor 43 runs at relatively high speed, drawing current at a correspondingly low rate due to the high back voltage generated by the armature 58 at the high speed. Thus, the current through the lamp 911 and the voltage drop across the lamp are low and the voltage applied to the base of the transistor 116 is proportionally low. The resulting opposition to the forward bias of the transistor is low and the transistor passes current at a relatively high rate. This current flow, in turn, produces a relatively high control torque opposing the biasing force of the shaft 110 tending to center the armature, and the latter rotates nearly to its full extent to displace the reversing valve spool a corresponding degree from its centered position, opening the feed orifices around the heads 95 and 97 relatively wide during each reversal. Consequently, the rate of flow of pilot fluid is high and the control valve spool shifts rapidly in response to each reversing signal to reverse the flow of fluid to the cylinder with a minimum delay after each reversal signal is produced. At this point in the honing cycle, the relatively light honing force exerted on the bore wall contributes least to the overcoming of the momentum of the tool head, and the greatest overshoot beyond the point of reversal point of the actuator occurs.

As the resistance to expansion of the tool 12 increases with the increasing area of engagement between the stones 34 and the wall 10, the feed motor armature 58 begins to slow down, generating less and less back voltage and drawing progressively higher current. This current increase raises the voltage drop across the lamp 91 (generally as the square of the current increases) and thus increases the input voltage at the transistor base to inplacement of the reversing valve spool, the size of the feed orifices 102, 103 that are opened, the rate of flow of pilot fluid to the chambers 1G4, 105 and, therefore, the rate of shift of the control valve spool. This progressively increases the delay between production of the reversal signal and actual reversal of the hydraulic actuator in direct relation to the increase in the drag on the tool. As a result, the control automatically counteracts the increasing tool drag to reverse the head 15 and the tool 12 at the same point at the end of each stroke. If the system pressure tends to increase with the honing force, the variation in size of the feed orifices also counteracts the tendency of the increasing pressure to accelerate the shift of the control valve spool.

I claim as my invention:

17 In a machine for honing the wall of a bore to en large the latter to a preselected size, the combination of, an expansible abrading tool, mechanism supporting said tool for back and forth reciprocation along said bore, mechanism for expanding said tool during such reciprocation including a variable torque electric feed motor, a tungsten filament incandescent lamp in series with the armature of, said feed motor and dropping the terminal voltage of said armature as the current drawn thereby increases with the resistance to expansion of said tool whereby said lamp modulates the progressively increasing torque and the resulting expanding force exerted by the motor during the honing cycle, a reciprocating hydraulic actuator connected to said tool and operable to reciprocate the latter back and forth through forward and return strokes within the bore, means producing a reversal signal as said tool approaches the end of each stroke and is a preselected distance from the end of the stroke, a fluid-operated control valve having a spool movable back and forth between spaced forward and reverse positions through an intermediate reversing position to reverse the flow through the valve in each direction of movement of the spool through said intermediate position, said control valve having two pressure chambers for pilot fluid for shifting said spool back and forth, a reversing valve having an inlet port, two outlet ports communicating with the respective pressure chambers, and a second spool movable in opposite directions from a centered position to open feed orifices each communicating between said inlet port and one of the outlet ports and thereby admit pilot fluid alternately into the respective pressure chambers, a reversible electric torque motor having an output member connected to said second spool and operable when energized in each direction to exert a control force on the latter varying with the degree of energization of the torque motor, means yieldably urging said spool to said centered position and opposing said control force in both directions of energization of said torque motor whereby the amount of displacement of said spool, the size of said feed orifices, and the resulting flow rates are determined by the degree of energization of the torque motor, means responsive to said reversal signals actuating said torque motor alternately in opposite directions as said tool approaches the end of each stroke, and means progressively reducing the degree of energization of said torque motor as said expanding force increases thereby progressively reducing the size of the feed orifices and delaying the effective reversal of said actuator by a progressively increasing amount.

2. The combination as defined in claim 1 in which said energization-reducing means is an element controlling the rate of current flow through said torque motor and operable in response to increases in the voltage drop across said lamp to correspondingly reduce said current flow and the resulting displacement of said spool.

3. The combination as defined in claim 2 in which said element is a transistor having a base to which a portion of said voltage drop is applied to increase the opposition to the forward bias of the transistor as the voltage drop increases.

4. In a machine for honing the wall of a bore to enlarge the latter to a preselected size, the combination of, an expansible abrading tool, mechanism supporting said tool for back and forth reciprocation Within said bore, mechanism for expanding said tool during such reciprocation and exerting a progressively increasing expanding force on the tool, a reciprocating hydraulic actuator connected to said tool and operable to reciprocate the latter through forward and return strokes Within the bore, means producing a reversal signal as the tool approaches the end of each stroke and is a preselected distance from the end of the stroke, a control valve for delivering pressure fluid alternately to opposite ends of said actuator and operable when actuated to reverse the direction of flow of said fluid, said valve having a valve member movable back and forth between two spaced operating positions through an intermediate reversing position to produce the alternating fluid flow, means sensing and indicating the magnitude of the expanding force exerted by said expanding mechanism and the resulting increase in the resistance to movement of said tool along said bore, means operating in response to each of said signals to shift said member from one operating position to the other, and means for reducing the rate of shift as said expanding force increases to delay reversal of said valve a progressively increasing amount as said resistance increases thereby maintaining the length of said strokes despite the increasing tendency of said resistance to stop the tool short.

5. The combination as defined in claim 4 in which said expanding mechanism includes a variable torque electric motor, and said sensing means is a device producing an electrical signal of varying magnitude indicating the rate of current flow through the motor armature thereby indicating the prevailing torque developed by the motor.

6. The combination as defined in claim 5 in which said device is a tungsten-filament incandescent lamp in series with said armature, and said electrical signal is the voltage drop across the lamp.

7. The combination as defined in claim 5 in which said control valve is operated by pilot pressure fluid, and said shifting means includes a reversing valve delivering an alternating flow of pilot fluid to the control valve through feed orifices that are progressively reduced in size as the magnitude of said electrical signal increases.

8. The combination as defined in claim 7 in which said shifting means also includes a reversible torque motor for operating said reversing valve and variably energized according to the magnitude of said electrical signal and in response to said reversal signals, said reversible torque motor having an output member connected to said reversing valve and displaced in each direction a distance correlated With the magnitude of said electrical signal to determine the size of said orifices.

9. In a machine for honing the wall of a bore to enlarge the latter to a preselected size, the combination of, an expansible abrading tool, mechanism supporting said tool for back and forth reciprocation within said bore, mechanism for expanding said tool during such reciprocation and exerting a progressively increasing expanding .force on the tool, a reciprocating hydraulic actuator connected to said tool and operable to reciprocate the latter through forward and return strokes within the bore, means producing a reversal signal as the tool approaches the end of each stroke and is a preselected distance from the end of the stroke, a control valve having a valve member movable back and forth between spaced forward and reverse positions and operable upon moving between said positions to reverse the flow of fluid to said actuator, means for initiating movement of said member from one position to the other in response to each of said signals, and means progressively reducing the rate of movement of said member between said positions as the resistance to movement of the tool along said bore increases and in direct relation with the increase in resistance thereby delaying eifective reversal of said actuator as the drag on said tool increases and maintaining said preselected distance substantially constant.

10. In a machine for honing the wall of a bore to enlarge the latter to a preselected size, the combination of, an expansible abrading tool, mechanism supporting said tool for back and forth reciprocation within said bore, mechanism for expanding said tool during such reciprocation and exerting a progressively increasing expanding force on the tool, a reciprocating actuator connected to said tool and operable to reciprocate the latter through forward and return strokes within the bore, means producing a reversal signal as the tool approaches the end of each stroke and is a preselected distance from the end of the stroke, means sensing and indicating the magnitude of the expanding force exerted by said expanding mechanism and the resulting increase in the resistance of movement of said tool along said bore, and means for reversing said actuator in response to each reversal signal after a time delay increasing with the magnitude of said resistance thereby to maintain the length of said strokes constant despite the increasing tendency of said resistance to stop the tool short.

11. The combination as defined in claim 10 in which said expanding mechanism includes an electric motor and said sensing means is a resistor in series with the armature of said motor, said resistor having a positive temperature coefiicient of resistance and a temperature that varies over a wide range with the rate of current flow whereby the magnitude of said expanding force is indicated by the voltage drop across the resistor.

12. The combination as defined in claim 11 in which said reversing means includes a motor variably energized in accordance with the magnitude of said voltage drop and operable to increase said delay in accordance with the increase in the voltage drop.

References Cited UNITED STATES PATENTS 2,164,811 7/1939 Floss 5134 2,381,572 8/1945 Caldwell 51 34 HAROLD D. WHITEHEAD, Primary Examiner. 

1. IN A MACHINE FOR HONING THE WALL OF A BORE TO ENLARGE THE LATTER TO A PRESELECTED SIZE, THE COMBINATION OF, AN EXPANSIBLE ABRADING TOOL, MECHANISM SUPPORTING SAID TOOL FOR BACK AND FORTH RECIPROCATION ALONG SAID BORE, MECHANISM FOR EXPANDING SAID TOOL DURING SUCH RECIPROCATION INCLUDING A VARIABLE TORQUE ELECTRIC FEED MOTOR, A TUNGSTEN FILAMENT INCANDESCENT LAMP IN SERIES WITH THE ARMATURE OF SAID FEED MOTOR AND DROPPING THE TERMINAL VOLTAGE OF SAID ARMATURE AS THE CURRENT DRAWN THEREBY INCREASES WITH THE RESISTANCE TO EXPANSION OF SAID TOOL WHEREBY SAID LAMP MODULATES THE PROGRESSIVELY INCREASING TORQUE AND THE RESULTING EXPANDING FORCE EXERTED BY THE MOTOR DURING THE HONING CYCLE, A RECIPROCATING HYDRAULIC ACTUATOR CONNECTED TO SAID TOOL AND OPERABLE TO RECIPROCATE THE LATTER BACK AND FORTH THROUGH FORWARD AND RETURN STROKES WITHIN THE BORE, MEANS PRODUCING A REVERSAL SIGNAL AS SAID TOOL APPROACHES THE END OF EACH STROKE AND IS A PRESELECTED DISTANCE FROM THE END OF THE STROKE, A FLUID-OPERATED CONTROL VALVE HAVING A SPOOL MOVABLE BACK AND FOURTH BETWEEN SPACED FORWARD AND REVERSE POSITIONS THROUGH AN INTERMEDIATE REVERSING POSITION TO REVERSE THE FLOW THROUGH THE VALVE IN EACH DIRECTION OF MOVEMENT OF THE SPOOL THROUGH SAID INTERMEDIATE POSITION, SAID CONTROL VALVE HAVING TWO PRESSURE CHAMBERS FOR PILOT FLUID FOR SHIFTING SAID SPOOL BACK AND FORTH, A REVERSING VALVE HAVING AN INLET PORT, TWO OUTLET PORTS COMMUNICATING WITH THE RESPECTIVE PRESSURE CHAMBERS, AND A SECOND SPOOL MOVABLE IN OPPOSITE DIRECTIONS FROM A CENTERED POSITION TO OPEN FEED ORIFICES EACH COMMUNICATING BETWEEN SAID INLET PORT AND ONE OF THE OUTLET PORTS AND THEREBY ADMIT PILOT FLUID ALTERNATELY INTO THE RESPECTIVE PRESSURE CHAMBERS, A REVERSIBLE ELECTRIC TORQUE MOTOR HAVING AN OUTPUT MEMBER CONNECTED TO SAID SECOND SPOOL AND OPERABLE WHEN ENERGIZED IN EACH DIRECTION TO EXERT A CONTROL FORCE ON THE LATTER VARYING WITH THE DEGREE OF ENERGIZATION OF THE TORQUE MOTOR, MEANS YIELDABLY URGING SAID SPOOL TO SAID CENTERED POSITION AND OPPOSING SAID CONTROL FORCE IN BOTH DIRECTIONS OF ENERGIZATION OF SAID TORQUE MOTOR WHEREBY THE AMOUNT OF DISPLACEMENT OF SAID SPOOL, THE SIZE OF SAID FEED ORIFICES, AND THE RESULTING FLOW RATES ARE DETERMINED BY THE DEGREE OF ENERGIZATION OF THE TORQUE MOTOR, MEANS RESPONSIVE TO SAID REVERSAL SIGNALS ACTUATING SAID TORQUE MOTOR ALTERNATELY IN OPPOSITE DIRECTIONS AS SAID TOOL APPROACHES THE END OF EACH STROKE, AND MEANS PROGRESSIVELY REDUCING THE DEGREE OF ENERGIZATION OF SAID TORQUE MOTOR AS SAID EXPANDING FORCE INCREASES THEREBY PROGRESSIVELY REDUCING THE SIZE OF THE FEED ORIFICES AND DELAYING THE EFFECTIVE REVERSAL OF SAID ACUTATOR BY A PROGRESSIVELY INCREASING AMOUNT. 